Resistance unit and method of making



F. H. BULLINGER. RESISTANCE UNlT AND METHOD 0F MAKING. APPLICATION FILEDv APR. 2?, 1920.

l ,404267.v Patented J an. 24, 1922.

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FREDERIC H. BULLINGER, OF YONXERS, NEW YORK,.ASSIGNOR TO WARD LEONARD ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

'RESISTANCE UNIT AND METHOD OF MAKING. l

To all whomt may' concern: l y Be it known that I, FREDERIC H. Bm.- LINGER, a citizenof the United States, residing at Yonkers, in the county of Westchester and State of New York, have invented certain new and useful Improvements in lResistance Units and Methods of Making, of which the following is a specification.

rlhis invention relates to resistance units or-rheostatic units, in which the resistance element or elements are imbedded in or covered by an insulating coating, such as vitreous enamel, or ,other coating, which is fused or baked in a furnace of comparatively high temperature. A

y In resistance units of this character, it is voften desired to provide rigid terminal connections'which form a part of the unit when completed, in order to afford conveni' ent contacts or terminals for the connection of external leads.

The main object of this invention is to provide an improved construction of the unit and method of making, which will insure good electrical contact of such terminals with the resistive conductor of the unit, and to accomplish this in a manner which lwill simplify the cost of manufacture, espe cially in the costof labor.

Devices of this character present a dificult problem in making connection between` the terminal and the resistive conductor. This is due to the comparatively high temperature of the furnace in baking or fusing the insulating coating, which high tem erature causes oxidation of the metals w ere they make contact and give a poor electrical connection or none at all in the completed article, unless special means are taken to insure the connection. One method heretofore employed is to place-a metal clip overv to make the tap connection before continu# inwiththe winding. Y u p V- y my present invention, the winding of the resistive conductor vmay be proceeded.

Specification of Letters IPatent.

with continuously and the taps applied afterwards which saves considerable time. Also I secure a good soldered joint between the resistive conductor and the terminal which is of a character that is not destroyed in the firing of the unit, and further cause the operation of baking or fusing the insu lating coating vto also makethe .soldered joint. I am furthermore enabled to locate the soldered joint under the terminal or tap connection where it is not only effectively soldered' but insures a protected permanent connection.

The accompanying drawings illustrate one form of unit embodying and made in accordance with my invention, Fig. l being a side elevation without the insulating coating applied andwith parts broken away; Fig. 2 anend view of Fig, 1; and Fig. 3 a side elevation of the unit complete.

In this instance a' tube l of earthenware, porcelain or like material is wound with Patented Jan. 24, 1922/. A Application led April 27, 1920. Serial Io. 377,012. I

the resistive wire Q. The terminals or tap nections, such as prolonging the extensions 3 for receiving additional terminal screws.

Before clamping the bands in place, I introduce a piece or sheet of solder 7 under each band and between it and the resistive conductor together with a suitable flux. This solder should'have a fusing point appreaching/or comparatively ,near the furnace temperature required to fuse or Jbake the'enamel coating. When the bands are clamped-.in place with the solder applied as above stated, it gives a firm contact of the solder` with the bands and resistive conductor. vThe insulating coating 8- of enamel or other suitable material is then applied to cover the resistive conductor and to cover wholly, or partially, the bands 3. The unit is then'ired or baked at lthe re uired temperature to fuse or bake the insu ating coating, which' operation also fuses the solder` to give a soldered connection and a'good permanent joint and electric connection bef tween the conductor and taps.

ln order to secure satisfactory results by 'this method, it is important that the solder .used shall havela fusing point approaching or comparatively near the temperature lto Awhich the insulating coating is subjected in baking or fusinor it. ln the case of fusing a vitreous enamel insulating coating, the temperature to which the unit `is commonly subjected in firing is from 600 to 700 degrees centigrade. lf the usual solders, which have a low fusing point, be used in such a case, even when soldered before firing or attempted to be soldered during firing, the high temperature of ,firing lwill cause such solder` to become very thin and run away from betWeen-the-conductor and taps and spoil the soldered joint. It also causes the adjoining parts of the joint to become oxidized and prevents an electrical connection or'permits'such a'poor one as to be unsatisfactory or lacking in permanence. vBy using a solder which has a high/fusing point and whichl apfproa'ches the ring temperature, the soldering may be accomplished during the firing;

because atthe hightemperature of firing,

the -solder softens. or melts sufficiently to make a goodtsoldered joint and maintains it during firing because it does not become or have the parts exposed to oxidation.

so thin as to run and spoil the soldered joint haveV obtained satisfactory results .with a solder composed of about 80 per cent tin and 20 per cent copper which fuses well the term enamel is used,v it includes any equivalent insulating coating.y

Although I havedescribed a preferred` embodiment and method of my invention,

vthis -inayv be modified without departing from the scope thereof. j.

I claim temperature, or

taps `in the appended -above 500 degrees centigrade; but other i 1. The method of making a resistance unit I which consists in applying the resistive con-A .ductor to a support', placing a tap in connection`with the conductor with solder interposed, ,applying a coating of enamel inaterial thereto, and heating the unitto simul vtaneously fuse the solder and enamel.

2. The method of making aresistance unit which consists in applying the resistive conductor to a support, clamping a tap against the conductor with. solder interposed, ysaid solder having a high fusing point, applying aV coating of enamel material thereto', and

heating the unit to simultaneously fuse the solder and enamel.

FREDERIC H. ABULLINenig:I 

